Etching of copper workpieces is generally accomplished in etching machines wherein the workpiece is placed on a conveyor and is transported into the etching machine for exposure to an industrial etchant. A commonly used etchant is a solution of cupric chloride. Although cupric chloride and other etchants are quite effective in etching metal from the workpiece, the etching procedure becomes gradually less efficient. There is a continuous reduction of the cupric (Cu.sup.+2) to cuprous (Cu.sup.+1) ions. Cuprous ions are totally ineffective as an etchant and have a tendency to retard the etching procedure. As the etching procedure continues, the concentration of copper in solution increases. This causes the concentration of cuprous ions to increase and results in a further decrease in the etching efficiency or speed. Thus, the continuous accretion of copper into the etching solution reduces the ability of the etchant to efficiently perform its functions.
Some etchants, particularly cupric chloride, change color as the etchant vigor deteriorates. A fresh solution of cupric chloride is a clear green color, but a spent solution, containing a substantial amount of cuprous chloride, turns brown because cuprous chloride, being insoluable, forms a brownish precipitate.
To compensate for the gradual degradation of etching efficiency, prior art systems have adopted methods to regenerate the etchant. Regeneration means that one component, such as copper, may be extracted and the fluid may be recycled through the etcher. Regeneration may also be accomplished by the addition of acid and oxidizer to reoxidize the cuprous chloride back to cupric chloride. The reoxidization regenerates the etchant to increase its vigor as an etchant.
The regenerative approach, in the prior art, has proven to be relatively costly. It requires investment in expensive apparatus. Furthermore, the components of regenerative systems occupy a very large part of the production space of industrial installations. Regenerative systems have been relatively complex and require frequent and careful maintenance. Many industrial installations are subject to variable or irregular work loads, and in such systems, the conventional regenerative approaches are of minimum assistance. Furthermore, where there is substantial variability in the work load, large portions of the regenerative components may be unused for extended periods of time.
There has been a need, therefore, to provide a regenerative system that efficiently regenerates the etchant so that it will efficiently etch production workpieces. There has also been a need for a regenerative system that continuously monitors the etchant composition and detects deterioration of the etchant. Furthermore, there has been a need for an effective regenerative system that is compact and relatively inexpensive.